1. Field of the Invention
This invention relates to a hydraulic chuck assembly for a tool machine, more particularly to a hydraulic chuck assembly with valve units to control flowing of pressurized fluids to move a piston between releasing and tightening positions.
2. Description of the Related Art
Referring to FIGS. 1 and 2, a conventional chuck assembly 10 disclosed in U.S. Pat. No. 6,668,859 is shown to include a housing 11, a mount 12, a valve sleeve 13, a valve unit 15, a bearing unit 16, a rotary unit 17, a piston 18, front and rear taper sockets 20,21, front and rear collet heads 22,23, and a connecting shaft 19.
The mount 12 is disposed within the housing 11, and has an axially-extending hole 121, fluid inlet and outlet ports 122,123 extending radially, and a fluid passage 124 disposed to permit fluid to flow into a fluid chamber 112 in the housing 11. The valve sleeve 13 is mounted in the axially-extending hole 121 for accommodating the valve unit 15, and has a valve inlet 133 fluidly communicated with the fluid inlet port 122, and a valve outlet 134. The valve unit 15 has a valve seat 152 fluidly communicated with the valve inlet 133, and a spring-loaded ball 154 biased to close the valve seat 152. The bearing unit 16 is disposed in the axially-extending hole 121 at front and rear sides of the valve unit 15. The rotary unit 17 extends axially through the bearing unit 16, and has a fluid duct 171 fluidly communicated with the valve outlet 134. The piston 18 is movably disposed in the rotary unit 17 to be moved away from the fluid duct 171 upon injection of high-pressure hydraulic fluid into the rotary unit 17 through the fluid inlet port 122 and the fluid duct 171. The front and rear taper sockets 20,21 are threadedly fastened to the rotary unit 17 and the piston 18, respectively. The front collet head 22 is movably received in the front taper socket 20. The rear collet head 23 is movably received in the rear taper socket 21, and is coupled to the front collet head 22 by the connecting shaft 19.
Movement of the piston 18 away from the fluid duct 171 results in concurrent actuation of the front and rear collet heads 22,23 through the front and rear taper sockets 20,21 so as to clamp a workpiece between the front and rear collet heads 22,23. However, the following drawbacks arise:
1. Since the spring-loaded ball 154 is mounted to move axially, it tends to disengage from the valve seat 152 by virtue of the centrifugal force during high-speed rotation of the chuck assembly 10, thereby resulting in oil leakage from the valve unit 15 so that the workpiece cannot be clamped reliably by the collet heads 22,23.
2. Since the clearance 14 disposed between the valve sleeve 13 and the mount 12 is relatively small (e.g. 0.03 mm-0.04 mm), and since the valve sleeve 13 and the mount 12 are disposed radially opposite to each other, the valve sleeve 13 and the mount 12 may be in contact with each other during high-speed rotation of the chuck assembly 10 to result in malfunction thereof.